Server 2016 RDS via Azure AD Application Proxy end-to-end guide

One of our priorities for this year was to improve our remote access offering to staff to enable more flexible working whilst outside of college. Office 365 helps greatly and has already improved functionality in many ways but there’s still some legacy applications and classic file shares that need to be provided remotely too. If at all possible we prefer the files not to leave the network so some form of virtual desktop looked the way to go.

After discounting VMware and Citrix offerings on cost grounds the improvements to Microsoft’s RDS offering in Server 2016 seemed to come at a perfect time.

Even more so now we’ve implemented Azure AD Application Proxy (more on that shortly!) We’ve also recently decommissioned some services that freed up a bit of physical hardware resource to “play” with so away we went!

Server installation

The physical hardware for now is running on some reclaimed Dell PowerEdge R610 servers; 64GB RAM, dual CPU and 6 x 15k disks in RAID10. Should be plenty to get us up and running with the RDS roles eventually split across two hosts. For now we’re running on just the one but even that’s plenty to get up and running with.

We installed Server 2016 Core running the Hyper-V role, which was simple enough. The Core role looks to be a tad more polished in Server 2016, although not new the sconfig tool got the main settings entered with fairly minimal fuss.

yes it will go back in the rack once we’re done with it!

Getting the OS to update correctly wasn’t so simple due to Microsoft doing something silly to the update mechanism in the initial release of Windows 10 1607 and its equivalent Server 2016 release. Update status was stuck on “Downloading” showing no signs of progressing. In the end manually installing the latest Cumulative update release from the Microsoft Update Catalog did the trick e.g.

Server roles

With Hyper-V up and running the next stage was to install our guests. We went with 3 VMs set up as follows:

Connection Broker \ RD Licensing

RD Web Access \ RD Gateway

RD Session Host

The original plan was to try and embrace the Server Core concept and only install the GUI where absolutely necessary. With that in mind we made the first two servers with Core and only the Session Host with a GUI. More on that soon… (!)

RDS deployment wizard Role Services

Running the deployment through Server Manager on my desktop was easy going, Microsoft have done good work with this and the deployment doesn’t seem too far removed from the 2012 R2 guides I’ve been looking at online. We added each server to the roles as per above, got to the final screen and hit the magic Deploy button then…

"Unable to install RD Web Access role service on server"Role service... FailedDeployment... Cancelled

Well that didn’t go to plan! We had a look online, trying to find reasons for the failures and went through some initial troubleshooting to make sure all recent updates were installed and each server’s patches matched exactly, also enabled Powershell remoting…

So it appears the RD Gateway \ RD Web Access role isn’t supported on Server Core. Of course we wouldn’t want the web-facing part of the deployment running on a server with reduced attack surface would we Microsoft… not impressed!

Published names & certificate fun and games

After begrudgingly re-installing one of the VMs with a GUI (seemed quicker than trying to convert the Core install) we managed to get past the final Deploy page with 3 success bars 🙂

The first key setting we were asked for was the external FQDN for the RD Gateway, which was added to our ISP-hosted DNS records. We use a wildcard certificate to cover our external facing SSL needs, nothing out the ordinary there and went on to apply it to each of the four roles specified by the RDS Deployment wizard. A Session Collection was created for a test group and pointed at the new Session Host. All looking promising.

The RD Gateway FQDN naming in itself wasn’t a problem but led us to an interesting part of the setup relating to SSL certificates and domains. Once we had the RDS services accessible from outside the network (see below) I fired up my 4G tethering to give it a test.

The connection worked but threw up a certificate warning and it was obvious to see why. Our wildcard certificate is for *.domain.ac.uk but the Connection Broker’s published FQDN is servername.subdomain.domain.ac.uk and therefore isn’t covered.

You’ll also need to ensure that you can access the new published name internally, depending on what form your internal domain is vs. your external you may need to do a bit of DNS trickery with zones to get the records you need. More on that can be found at:

When done the end result is a seamless login to RD Web Access via the Azure AD login page. In our case the link will eventually end up as a button on our Office 365-based Staff Intranet, therefore not requiring any further logins to get to the RDWeb app selection screen.

I particularly wanted to avoid the RDWeb login screen, which I’m amazed in 2017 still requires DIY hacks to avoid the requirement to login with the DOMAIN\username format. Thought Microsoft would’ve improved that in the Server 2016 release but evidently not.

One more gotcha

So having done all the hard work above preparing the login all that was left was to click the Remote Desktop icon and enjoy, right? Wrong.

After running the Set-RDPublishedName script the certificate warning went away and I could see the change to the new wildcard-friendly name, however the connection attempt now failed with the error “Remote Desktop can’t connect to the remote computer *connectionbrokername* for one of these reasons”

connection failure after changing Published Name

Neither explanation made any sense as the connection was working perfectly fine until changing the Published Name. Indeed changing it back to the original FQDN of the Connection Broker restored service so it had to be something to do with that. After being stumped initially I came back after food (always helps!) then after a bit more research found this very helpful post:

It turns out the new FQDN we added when changing the Published Name needs to be added to RDG_RDAllConnectionBrokers Local Computer Group.

This group is used to approve connections in the Resource Authorization Policies (RD-RAP) section of RD Gateway Manager. By default only the server’s domain FQDN is present in the list (as you’d expect) so it appears unless you add the new Published Name in there the connection attempt gets denied.

type the FQDN of the Published Name you supplied to the Powershell script earlier then click Add

OK all the way out then try your connection again

RD Gateway Manager

The example below replaces the real server names with dummy entries but should illustrate the concept. The same scenario applies if your servers exist in a .local Active Directory domain (which will be the top entry) and your external domain is something different (again remember to sort out internal DNS zone entries to suit)

Manage RDG_RDCBComputers group

Finishing touches

Once all the above is done you should then get a connection, there is one seemingly unavoidable credential prompt due to Microsoft persisting with using an ActiveX control to start the RDP session but perhaps one day they’ll update it (we live in hope). It seems you can use the UPN style format here which is handy as it keeps things consistent. In a way it’s a bit of a security measure so not the end of the world.

Now the connection itself is sorted out all that’s left is to tweak the Session Host to our requirements. This guide gives some nice pointers on locking down the server via GPO:

We also push out a custom Start Menu using the newer Windows 10 1607 GPO settings along with the Export-StartLayout command. Finally install any programs required, remember to change the mode of the server first:

Great article, thank you for your time.
Any comments on protecting the gateway with 2FA?
Most people like myself, looking at Application proxy to enable AzureAD 2FA for RDS. However, with the above setup, if the user simply saves the RDP file to their computer, they can instead, click on this file and totally bypass RDWEB, and therefore 2FA. This is a major hole in the design, which doesn’t appear to be addressed anywhere that I can see?

Unfortunately we don’t have the Azure AD Premium licenses to try it so will be interested to hear how you get on.

Also hoping the as-yet-unreleased Server 2016 update with HTML5 support will give us native integration with Azure AD (and therefore MFA) out the box. Was meant to be part of Server 2016 1709 but seemed to get held back 😦

Making IT work

Welcome to my blog, my name is Gerrard Shaw, currently working as a Network Support Officer at Havering College of Further and Higher Education.

I'll be focusing on new developments with Office 365, Windows, Moodle and server \ networking technologies. I'm a great believer in sharing best practice and contributing to the wider technical community so hope you'll find something of interest...